PWM DC-DC converter with linear voltage regulator for DC assist

ABSTRACT

A DC power supply, which includes a DC-DC converter and a linear voltage regulator, is disclosed. The DC-DC converter provides a DC power supply signal and a duty-cycle signal, which is based on a duty-cycle of the DC-DC converter. The DC-DC converter provides the DC power supply signal via a power supply output using a setpoint of the DC power supply. The linear voltage regulator provides a DC assist signal to assist the DC-DC converter when an adjusted setpoint of the DC power supply is greater than a voltage of the DC power supply signal. The linear voltage regulator provides the adjusted setpoint using the setpoint and the duty-cycle signal, such that the adjusted setpoint is directly related to the setpoint and to the duty-cycle.

FIELD OF THE DISCLOSURE

The present invention relates to pulse width modulation (PWM) directcurrent (DC)-DC converters, which may be used in radio frequency (RF)communications systems.

BACKGROUND

Traditional 2^(nd) generation (2G) global system for mobilecommunications (GSM) cellphones, or other user equipment, may typicallybe battery powered using traditional high-power, high current, low-cost,and low drop-out (LDO) regulators. However, in applications having highefficiency requirements, linear DC power supplies may be inadequatebecause the efficiency of a linear voltage regulator degradesdramatically the more the linear regulator output voltage is below thebattery voltage. As a result, a DC power supply, which includes a DC-DCconverter and a linear voltage regulator, may be preferred. The linearvoltage regulator may provide high output current when the outputvoltage approaches the battery voltage, and the DC-DC converter mayprovide high efficiency when the battery voltage is greater than theoutput voltage. In this regard, a 2G GSM cellphone may benefit from sucha power supply. In general, for 2G cellular applications there is a needfor a DC power supply having a combination of a DC-DC converter and alinear voltage regulator.

SUMMARY

A DC power supply, which includes a DC-DC converter and a linear voltageregulator, is disclosed according to one embodiment of the presentdisclosure. The DC-DC converter provides a DC power supply signal to aload via a power supply output and a duty-cycle signal, which is basedon the load. The linear voltage regulator provides assistance to theDC-DC converter when the DC-DC converter is incapable of supplying theload by itself.

In this regard, the DC power supply operates in either a normal mode oran assist mode. The normal mode is selected when the DC-DC converter iscapable of supplying the load by itself. As such, during the normalmode, the DC-DC converter provides the duty-cycle signal to place thelinear voltage regulator in a stand-by mode and supplies power to theload by itself.

Conversely, the assist mode is selected when DC-DC converter needsassistance from the linear voltage regulator.

In an example embodiment of the present disclosure, the normal mode isselected when an output voltage from the DC power supply is between 300and 400 millivolts below a battery voltage.

Those skilled in the art will appreciate the scope of the presentdisclosure and realize additional aspects thereof after reading thefollowing detailed description of the preferred embodiments inassociation with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The accompanying drawing figures incorporated in and forming a part ofthis specification illustrate several aspects of the disclosure, andtogether with the description serve to explain the principles of thedisclosure.

FIG. 1 shows a DC power supply according to one embodiment of the DCpower supply.

FIG. 2 shows details of a DC-DC converter illustrated in FIG. 1according to one embodiment of the DC-DC converter.

FIG. 3 shows details of the DC-DC converter illustrated in FIG. 1according to an alternate embodiment of the DC-DC converter.

FIG. 4 shows details of the DC-DC converter illustrated in FIG. 1according to an additional embodiment of the DC-DC converter.

FIG. 5 shows details of a linear voltage regulator illustrated in FIG. 1according to one embodiment of the linear voltage regulator.

FIG. 6 shows details of the linear voltage regulator illustrated in FIG.1 according to an alternate embodiment of the linear voltage regulator.

FIG. 7 shows an RF communications system according to one embodiment ofthe RF communications system.

FIG. 8 shows the RF communications system according to an alternateembodiment of the RF communications system.

DETAILED DESCRIPTION

The embodiments set forth below represent the necessary information toenable those skilled in the art to practice the embodiments andillustrate the best mode of practicing the embodiments. Upon reading thefollowing description in light of the accompanying drawing figures,those skilled in the art will understand the concepts of the disclosureand will recognize applications of these concepts not particularlyaddressed herein. It should be understood that these concepts andapplications fall within the scope of the disclosure and theaccompanying claims.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present disclosure. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

It will be understood that when an element such as a layer, region, orsubstrate is referred to as being “on” or extending “onto” anotherelement, it can be directly on or extend directly onto the other elementor intervening elements may also be present. In contrast, when anelement is referred to as being “directly on” or extending “directlyonto” another element, there are no intervening elements present.Likewise, it will be understood that when an element such as a layer,region, or substrate is referred to as being “over” or extending “over”another element, it can be directly over or extend directly over theother element or intervening elements may also be present. In contrast,when an element is referred to as being “directly over” or extending“directly over” another element, there are no intervening elementspresent. It will also be understood that when an element is referred toas being “connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present.

Relative terms such as “below” or “above” or “upper” or “lower” or“horizontal” or “vertical” may be used herein to describe a relationshipof one element, layer, or region to another element, layer, or region asillustrated in the Figures. It will be understood that these terms andthose discussed above are intended to encompass different orientationsof the device in addition to the orientation depicted in the Figures.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes,” and/or “including” when used herein specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms used herein should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthis specification and the relevant art and will not be interpreted inan idealized or overly formal sense unless expressly so defined herein.

A DC power supply, which includes a DC-DC converter and a linear voltageregulator, is disclosed according to one embodiment of the presentdisclosure. The DC-DC converter provides a DC power supply signal to aload via a power supply output and a duty-cycle signal, which is basedon the load. The linear voltage regulator provides assistance to theDC-DC converter when the DC-DC converter is incapable of supplying theload by itself.

In this regard, the DC power supply operates in either a normal mode oran assist mode. The normal mode is selected when the DC-DC converter iscapable of supplying the load by itself. As such, during the normalmode, the DC-DC converter provides the duty-cycle signal to place thelinear voltage regulator in a stand-by mode and supplies power to theload by itself. Conversely, the assist mode is selected when DC-DCconverter needs assistance from the linear voltage regulator.

In an example embodiment of the present disclosure, the normal mode isselected when an output voltage from the DC power supply is between 300and 400 millivolts below a battery voltage.

FIG. 1 shows a DC power supply 10 and a DC power source 12 according toone embodiment of the DC power supply 10 and the DC power source 12. Inone embodiment of the DC power source 12, the DC power source 12 is abattery. The DC power source 12 provides a DC source signal VDC to theDC power supply 10. The DC source signal VDC has a DC source voltageDCV. In addition, the DC power supply 10 has a power supply output PCP.The DC power supply 10 provides a DC power supply signal PPS via thepower supply output PCP using the DC source signal VDC. The DC powersupply signal PPS has a DC power supply voltage PPV. In addition, the DCpower supply 10 provides the DC power supply signal PPS using a setpointof the DC power supply 10.

The DC power supply 10 includes a DC-DC converter 14 and a linearvoltage regulator 16. In one embodiment of the DC-DC converter 14, theDC-DC converter 14 functions as a switching power supply, such that theDC-DC converter 14 has a duty-cycle. In one embodiment of the linearvoltage regulator 16, the linear voltage regulator 16 functions as ananalog power supply. In one embodiment of the DC-DC converter 14 and thelinear voltage regulator 16, the DC-DC converter 14 provides power moreefficiently than the linear voltage regulator 16, such that anefficiency of the DC-DC converter 14 is greater than an efficiency ofthe linear voltage regulator 16. Each of the DC-DC converter 14 and thelinear voltage regulator 16 receives a power supply control signal VRMP,which is representative of the setpoint of the DC power supply 10.

In one embodiment of the linear voltage regulator 16, when the DC sourcevoltage DCV minus the setpoint of the DC power supply 10 is greater thana voltage threshold, the DC-DC converter 14 disables the DC assistsignal DCA to reduce power output of the linear voltage regulator 16. Ina first embodiment of the voltage threshold, the voltage threshold isequal to 150 millivolts. In a second embodiment of the voltagethreshold, the voltage threshold is equal to 250 millivolts. In a thirdembodiment of the voltage threshold, the voltage threshold is equal to350 millivolts. In a fourth embodiment of the voltage threshold, thevoltage threshold is equal to 450 millivolts. In a fifth embodiment ofthe voltage threshold, the voltage threshold is equal to 550 millivolts.

In one embodiment of the DC-DC converter 14, the DC-DC converter 14provides the DC power supply signal PPS using the DC source signal VDCand using the setpoint of the DC power supply 10. In one embodiment ofthe linear voltage regulator 16, the linear voltage regulator 16provides a DC assist signal DCA to assist the DC-DC converter 14 usingthe DC source signal VDC. As such, the DC power source 12 provides theDC source signal VDC to both the DC-DC converter 14 and the linearvoltage regulator 16. The DC-DC converter 14 provides the DC powersupply signal PPS via the power supply output PCP and the linear voltageregulator 16 provides the DC assist signal DCA via the power supplyoutput PCP.

Each of the DC-DC converter 14 and the linear voltage regulator 16receives a feedback signal FBS via the power supply output PCP. As such,the feedback signal FBS is representative of the DC power supply signalPPS. The DC-DC converter 14 further provides a duty-cycle signal DCS tothe linear voltage regulator 16 based on the duty-cycle of the DC-DCconverter 14. In one embodiment of the linear voltage regulator 16, thelinear voltage regulator 16 provides the DC assist signal DCA to assistthe DC-DC converter 14 via the power supply output PCP when an adjustedsetpoint is greater than the DC power supply voltage PPV. In addition,the linear voltage regulator 16 provides the adjusted setpoint of the DCpower supply 10 using the setpoint and the duty-cycle signal DCS, suchthat the adjusted setpoint is directly related to the setpoint anddirectly related to the duty-cycle of the DC-DC converter 14. In analternate embodiment of the linear voltage regulator 16, the linearvoltage regulator 16 provides the DC assist signal DCA to assist theDC-DC converter 14 via the power supply output PCP when an adjustedsetpoint is within an assist range of the DC power supply signal PPS.

In one embodiment of the DC-DC converter 14 and the linear voltageregulator 16, when the duty-cycle of the DC-DC converter 14 is less thana maximum duty-cycle, the adjusted setpoint is less than the setpoint.In one embodiment of the DC-DC converter 14 and the linear voltageregulator 16, the maximum duty-cycle is equal to 100 percent. In oneembodiment of the DC-DC converter 14 and the linear voltage regulator16, when the duty-cycle of the DC-DC converter 14 is essentially equalto the maximum duty-cycle, the adjusted setpoint is essentially equal tothe setpoint. In an exemplary embodiment of the DC-DC converter 14, whenthe duty-cycle of the DC-DC converter 14 is equal to zero, a portion ofthe DC power supply voltage PPV that is provided by the DC-DC converter14 is equal to essentially zero volts. When the duty-cycle of the DC-DCconverter 14 is equal to 100 percent, the portion of the DC power supplyvoltage PPV that is provided by the DC-DC converter 14 is equal toessentially the DC source voltage DCV. When the duty-cycle is betweenzero and 100 percent, the portion of the DC power supply voltage PPVthat is provided by the DC-DC converter 14 varies based on theduty-cycle signal DCS. In this regard, the adjusted setpoint is used tocontrol the assistance that is provided by the linear voltage regulator16.

FIG. 2 shows details of the DC-DC converter 14 illustrated in FIG. 1according to one embodiment of the DC-DC converter 14. The DC-DCconverter 14 includes an error voltage clamping circuit 18, a convertererror amplifier 20, a pulse-width modulation controller 22, a chargepump 24, a first lowpass filter 26, and a dithering clock generator 28.The converter error amplifier 20 receives the power supply controlsignal VRMP and the feedback signal FBS via the error voltage clampingcircuit 18. As such, the converter error amplifier 20 provides an errorsignal ERR based on a difference between the power supply control signalVRMP and the feedback signal FBS.

In general, the DC-DC converter 14 provides the DC power supply signalPPS using the error signal ERR. Since the feedback signal FBS is basedon the DC power supply signal PPS and since the power supply controlsignal VRMP is representative of the setpoint of the DC power supply 10,the error signal ERR is indicative of the accuracy of the DC powersupply signal PPS with respect to the setpoint of the DC power supply10.

The error signal ERR is used to control the pulse-width modulationcontroller 22, which provides a charge pump control signal CPC based onthe error signal ERR and a clock signal CLK, which is provided by thedithering clock generator 28. The charge pump control signal CPC is usedto control the charge pump 24. In this regard, in one embodiment of thepulse-width modulation controller 22, a frequency of the charge pumpcontrol signal CPC is based on the frequency of the clock signal CLK. Inone embodiment of the DC-DC converter 14, the dithering clock generator28 dithers a frequency of the clock signal CLK to dither a frequency ofthe charge pump control signal CPC and a frequency of the duty-cyclesignal DCS. Dithering the frequency of the charge pump control signalCPC dithers a frequency of a switching output signal SWT. Dithering thefrequency of the switching output signal SWT may reduce output noise ofthe DC-DC converter 14.

However, in one embodiment of the pulse-width modulation controller 22,when the error signal ERR has a constant maximum value, the charge pumpcontrol signal CPC has a constant maximum value. Conversely, when theerror signal ERR has a constant minimum value, the charge pump controlsignal CPC has a constant minimum value. Otherwise, a frequency of thecharge pump control signal CPC is based on the frequency of the clocksignal CLK, such that a duty-cycle of the charge pump control signal CPCis based on the error signal ERR. In addition, the pulse-widthmodulation controller 22 provides the duty-cycle signal DCS, such thatthe duty-cycle of the duty-cycle signal DCS is based on the duty-cycleof the charge pump control signal CPC.

The error voltage clamping circuit 18 is coupled to inputs to theconverter error amplifier 20. The error voltage clamping circuit 18receives the power supply control signal VRMP and the feedback signalFBS and limits the difference between the power supply control signalVRMP and the feedback signal FBS that is presented to the convertererror amplifier 20. By limiting the difference between the power supplycontrol signal VRMP and the feedback signal FBS presented to theconverter error amplifier 20, the error voltage clamping circuit 18allows fast recovery of the DC-DC converter 14 when the differencebetween the power supply control signal VRMP and the feedback signal FBSis large.

The charge pump 24 receives the charge pump control signal CPC andprovides the switching output signal SWT based on the charge pumpcontrol signal CPC. The charge pump 24 includes at least one energystorage element, such as one or more capacitive element. The firstlowpass filter 26 receives and filters the switching output signal SWTto provide the DC power supply signal PPS.

FIG. 3 shows details of the DC-DC converter 14 illustrated in FIG. 1according to an alternate embodiment of the DC-DC converter 14. TheDC-DC converter 14 illustrated in FIG. 3 is similar to the DC-DCconverter 14 illustrated in FIG. 2, except in the DC-DC converter 14illustrated in FIG. 3, the error voltage clamping circuit 18 is omittedand the dithering clock generator 28 is replaced with a clock generator30, such that the frequency of the clock signal CLK is not dithered. Assuch, the frequency of the charge pump control signal CPC is notdithered and the frequency of the duty-cycle signal DCS is not dithered.By omitting the error voltage clamping circuit 18, recovery time may beunacceptably long when the difference between the power supply controlsignal VRMP and the feedback signal FBS is large.

FIG. 4 shows details of the DC-DC converter 14 illustrated in FIG. 1according to an additional embodiment of the DC-DC converter 14. TheDC-DC converter 14 illustrated in FIG. 4 is similar to the DC-DCconverter 14 illustrated in FIG. 3, except the DC-DC converter 14illustrated in FIG. 4 further includes a regulator efficiency monitor32. The regulator efficiency monitor 32 receives the power supplycontrol signal VRMP and the DC source signal VDC. The regulatorefficiency monitor 32 provides a regulator disable signal RDS to thepulse-width modulation controller 22 based on a difference between theDC source voltage DCV (FIG. 1) and the power supply control signal VRMP.In this regard, when the setpoint for the DC power supply voltage PPV(FIG. 1) is significantly less than the DC source voltage DCV (FIG. 1),the regulator efficiency monitor 32 disables the linear voltageregulator 16 (FIG. 1) using the regulator disable signal RDS. As such,the pulse-width modulation controller 22 disables the linear voltageregulator 16 (FIG. 1) via the duty-cycle signal DCS based on theregulator disable signal RDS.

In one embodiment of the DC-DC converter 14, when the setpoint for theDC power supply voltage PPV (FIG. 1) is at least 350 millivolts lessthan the DC source voltage DCV (FIG. 1), the regulator efficiencymonitor 32 disables the linear voltage regulator 16 (FIG. 1) using theregulator disable signal RDS. In one embodiment of the DC-DC converter14, when the setpoint for the DC power supply voltage PPV (FIG. 1) is atleast 400 millivolts less than the DC source voltage DCV (FIG. 1), theregulator efficiency monitor 32 disables the linear voltage regulator 16(FIG. 1) using the regulator disable signal RDS.

FIG. 5 shows details of the linear voltage regulator 16 illustrated inFIG. 1 according to one embodiment of the linear voltage regulator 16.The linear voltage regulator 16 illustrated in FIG. 5 includes an erroramplifier 34, a P-type field effect transistor (PFET) 36, a firstresistive element R1, and a second resistive element R2. The DC powersource 12 (FIG. 1) provides the DC source signal VDC (FIG. 1) to theerror amplifier 34 and to a source of the PFET 36. An inverting input ofthe error amplifier 34 receives the power supply control signal VRMP(FIG. 1). The first resistive element R1 is coupled between anon-inverting input to the error amplifier 34 and the power supplyoutput PCP (FIG. 1). The second resistive element R2 is coupled betweenthe non-inverting input to the error amplifier 34 and ground.

The error amplifier 34 receives the duty-cycle signal DCS via thenon-inverting input to the error amplifier 34. In one embodiment of theduty-cycle signal DCS, the duty-cycle signal DCS is a current signal,such that a magnitude of the duty-cycle signal DCS is inversely relatedto the duty-cycle of the DC-DC converter 14.

An output from the error amplifier 34 is coupled to a gate of the PFET36. The linear voltage regulator 16 provides the DC assist signal DCAvia a drain of the PFET 36. The PFET 36 provides an open-drain output ofthe linear voltage regulator 16, such that the open-drain output of thelinear voltage regulator 16 is coupled to the power supply output PCP(FIG. 1). The linear voltage regulator 16 provides the DC assist signalDCA via the open-drain output of the linear voltage regulator 16. ThePFET 36 is coupled between the error amplifier 34 and the power supplyoutput PCP (FIG. 1). The linear voltage regulator 16 provides the DCassist signal DCA via the error amplifier 34 and the PFET 36.

FIG. 6 shows details of the linear voltage regulator 16 illustrated inFIG. 1 according to an alternate embodiment of the linear voltageregulator 16. The linear voltage regulator 16 illustrated in FIG. 6 issimilar to the linear voltage regulator 16 illustrated in FIG. 5, exceptthe linear voltage regulator 16 illustrated in FIG. 6 includes a PNPbipolar junction transistor (BJT) 38 instead of the PFET 36 (FIG. 5).

In this regard, the DC power source 12 (FIG. 1) provides the DC sourcesignal VDC (FIG. 1) to the error amplifier 34 and to an emitter of thePNP BJT 38. An output from the error amplifier 34 is coupled to a baseof the PNP BJT 38. The linear voltage regulator 16 provides the DCassist signal DCA via a collector of the PNP BJT 38. The PNP BJT 38provides an open-collector output of the linear voltage regulator 16,such that the open-collector output of the linear voltage regulator 16is coupled to the power supply output PCP (FIG. 1). The linear voltageregulator 16 provides the DC assist signal DCA via the open-collectoroutput of the linear voltage regulator 16. The PNP BJT 38 is coupledbetween the error amplifier 34 and the power supply output PCP (FIG. 1).The linear voltage regulator 16 provides the DC assist signal DCA viathe error amplifier 34 and the PNP BJT 38.

FIG. 7 shows an RF communications system 100 according to one embodimentof the present disclosure. The RF communications system 100 includes RFtransmitter circuitry 102, RF system control circuitry 104, RF front-endcircuitry 106, an RF antenna 108, and the DC power source 12. The RFtransmitter circuitry 102 includes an RF PA 110 and the DC power supply10.

In one embodiment of the RF communications system 100, the RF front-endcircuitry 106 receives via the RF antenna 108, processes, and forwardsan RF receive signal RFR to the RF system control circuitry 104. The RFsystem control circuitry 104 provides the power supply control signalVRMP to the DC power supply 10. The RF system control circuitry 104provides an RF input signal RFN to the RF PA 110. In this regard, the RFsystem control circuitry 104 provides the setpoint of the DC powersupply 10 using the power supply control signal VRMP.

The DC power supply 10 provides power to the RF PA 110 using the DCpower supply signal PPS. The DC power supply signal PPS has the DC powersupply voltage PPV. In one embodiment of the power supply control signalVRMP, the power supply control signal VRMP is representative of asetpoint of the DC power supply signal PPS. The RF PA 110 receives andamplifies the RF input signal RFN to provide an RF transmit signal RFTusing the DC power supply signal PPS. In one embodiment of the DC powersupply 10, the DC power supply 10 provides power for amplification viathe DC power supply signal PPS. The RF front-end circuitry 106 receives,processes, and transmits the RF transmit signal RFT via the RF antenna108.

In one embodiment of the RF PA 110, the RF transmit signal RFT isamplitude modulated, such that the RF transmit signal RFT has anenvelope. In one embodiment of the DC power supply 10, the DC powersupply 10 modulates the DC power supply signal PPS to at least partiallytrack the envelope of the RF transmit signal RFT, thereby providingenvelope tracking. As such, in one embodiment of the RF system controlcircuitry 104, the RF system control circuitry 104 uses the power supplycontrol signal VRMP to modulate the DC power supply signal PPS. In oneembodiment of the RF transmit signal RFT, the RF transmit signal RFT isa second generation wireless telephone transmit signal.

FIG. 8 shows the RF communications system 100 according to an alternateembodiment of the RF communications system 100. The RF communicationssystem 100 illustrated in FIG. 8 is similar to the RF communicationssystem 100 illustrated in FIG. 7, except in the RF communications system100 illustrated in FIG. 8, the RF transmitter circuitry 102 furtherincludes a digital communications interface 112, which is coupledbetween the DC power supply 10 and a digital communications bus 114. Thedigital communications bus 114 is also coupled to the RF system controlcircuitry 104. As such, the RF system control circuitry 104 provides thepower supply control signal VRMP (FIG. 7) to the DC power supply 10 viathe digital communications bus 114. The DC power source 12 (FIG. 7) isnot shown to simplify FIG. 8.

Those skilled in the art will recognize improvements and modificationsto the preferred embodiments of the present disclosure. All suchimprovements and modifications are considered within the scope of theconcepts disclosed herein and the claims that follow.

What is claimed is:
 1. A Direct Current (DC) power supply comprising: aDC-DC converter configured to: provide a DC power supply signal to aload via a power supply output using a setpoint of the DC power supply;and provide a duty-cycle signal that is a current signal based on aduty-cycle of the DC-DC converter, such that a magnitude of theduty-cycle signal is inversely related to the duty-cycle; and a linearvoltage regulator coupled to the power supply output and configured to:receive the duty-cycle signal from the DC-DC converter; provide anadjusted setpoint of the DC power supply using the setpoint and theduty-cycle signal, wherein the adjusted setpoint is directly related tothe setpoint and directly related to the duty-cycle; and provide a DCassist signal to assist the DC-DC converter when the adjusted setpointis within an assist range of the DC power supply signal.
 2. The DC powersupply of claim 1 wherein the linear voltage regulator comprises anopen-drain output coupled to the power supply output, such that thelinear voltage regulator is further configured to provide the DC assistsignal via the open-drain output.
 3. The DC power supply of claim 1wherein the linear voltage regulator comprises an open-collector outputcoupled to the power supply output, such that the linear voltageregulator is further configured to provide the DC assist signal via theopen-collector output.
 4. The DC power supply of claim 1 wherein thelinear voltage regulator comprises an error amplifier and a transistorelement, such that the transistor element is coupled between the erroramplifier and the power supply output, and the linear voltage regulatoris further configured to provide the DC assist signal via the erroramplifier and the transistor element.
 5. The DC power supply of claim 4wherein the linear voltage regulator further comprises a first resistiveelement and a second resistive element, wherein the first resistiveelement is coupled between an input to the error amplifier and the powersupply output, and the second resistive element is coupled between theinput to the error amplifier and ground.
 6. The DC power supply of claim4 wherein the error amplifier receives the duty-cycle signal via aninput to the error amplifier.
 7. The DC power supply of claim 1 whereinwhen the duty-cycle is less than a maximum duty-cycle, the adjustedsetpoint is less than the setpoint.
 8. The DC power supply of claim 7wherein the maximum duty-cycle is equal to 100 percent.
 9. The DC powersupply of claim 7 wherein when the duty-cycle is equal to the maximumduty-cycle, the adjusted setpoint is equal to the setpoint.
 10. The DCpower supply of claim 1 wherein a DC power source is configured toprovide a DC source signal, such that the DC-DC converter is furtherconfigured to use the DC source signal to provide the DC power supplysignal and the linear voltage regulator is further configured to use theDC source signal to provide the DC assist signal.
 11. The DC powersupply of claim 10 wherein the DC power source is a battery.
 12. The DCpower supply of claim 10 wherein the DC source signal has a DC sourcevoltage, such that when the DC source voltage minus the setpoint isgreater than a voltage threshold, the DC-DC converter is furtherconfigured to disable the DC assist signal.
 13. The DC power supply ofclaim 12 wherein the voltage threshold is greater than 350 millivolts.14. The DC power supply of claim 1 wherein the DC-DC convertercomprises: a converter error amplifier configured to provide an errorsignal based on a difference between a feedback signal and a powersupply control signal; and a pulse-width modulation controllerconfigured to provide the duty-cycle signal to the linear voltageregulator and provide a charge pump control signal, wherein: the powersupply control signal is representative of the setpoint; the feedbacksignal is representative of the DC power supply signal; and the DC-DCconverter is further configured to provide the DC power supply signalusing the error signal.
 15. The DC power supply of claim 14 wherein theDC-DC converter further comprises an error voltage clamping circuitcoupled to the converter error amplifier and configured to receive thefeedback signal and the power supply control signal to limit thedifference between the feedback signal and the power supply controlsignal.
 16. The DC power supply of claim 14 wherein the DC-DC converterfurther comprises a dithering clock generator configured to provide aclock signal to the pulse-width modulation controller, wherein thecharge pump control signal is based on the clock signal and thedithering clock generator is further configured to dither a frequency ofthe clock signal to dither a frequency of the charge pump controlsignal.
 17. The DC power supply of claim 1 wherein control circuitry isconfigured to provide the setpoint of the DC power supply using a powersupply control signal.
 18. The DC power supply of claim 17 furtherconfigured to provide power to a radio frequency (RF) power amplifier(PA) using the DC power supply signal.
 19. The DC power supply of claim18 wherein the RF PA is configured to receive and amplify an RF inputsignal to provide an RF transmit signal using the DC power supplysignal.